Field
This application relates to a diagnostic system. In particular, this application describes a system and method for performing diagnostics on a transformer.
Description of Related Art
High voltage transformers are utilized in the delivery of power and are commonly utilized to step down voltages present on transmission lines to voltages more suitable for residential or commercial areas. Transformers generally include one or more primary windings and one or more secondary windings. In the case of a 3-phase electrical system, the primary windings may comprise three windings, each of which is coupled to a different phase of the electrical system.
The voltage delivered to a load is somewhat dependent on the load itself. Therefore, some high voltage transformers incorporate a load-tap-changer (LTC) and/or a de-energized tap changer (DETC). LTCs and DETCs are a switch mechanism that facilitate changing the turns ratio of the transformer. LTC/DETCs change position to control its output voltage.
High voltage transformers tend to undergo a large amount of stress during operation. This is especially the case during periods of peak-power usage, such as during warm days in the summer. The stress may result in degradation in the performance of the transformer. For example, insulation between the windings may degrade; shorts may begin to develop between adjacent turns or windings. Other problems may occur. If these problems persist for long enough, the transformer may catastrophically fail. This failure may, in turn, cause other components of the power system to fail.
In an attempt to minimize these sorts of disruptions, transformers typically undergo routine diagnostic testing after being installed to ascertain whether there are any issues that may lead to an eventual catastrophic failure. One test employed is to energize the windings or phases of the transformer with an AC voltage and to measure the magnitude of the power frequency component of the excitation current flowing into the transformer.
Unfortunately, experience has shown that this type of testing methodology does not always succeed in identifying a problem. In about 20-30% of cases the questions remain as to the location and the nature of the problem. Furthermore, the questions sometimes arise whether the change in the measured parameters is actually caused by a problem in a transformer.